What determines the time to gypsum adoption to remediate irrigated salt-affected agricultural lands? Evidence from Punjab, Pakistan

Highlights

• Gypsum application improves soil structure and health in Punjab, Pakistan.

• 56% of sampled farm households were gypsum adopters.

• Technology exposure, credit access, and legal land entitlement accelerate adoption.

• Gypsum application increases wheat and rice yields by 17% and 23%.

• Distance to input markets and soil testing laboratories decrease adoption speed.

Abstract

Soil salinization is a serious environmental problem in arid and semi-arid regions, affecting crop yields and jeopardizing the food security of affected households. A common prescription to ameliorate salt-affected soils is the application of gypsum. However, little is known about the factors that motivate land managers to adopt gypsum and its likely effect on crop yields in different agro-ecological and socio-economic contexts. This study investigates the gypsum adoption process to rehabilitate irrigated salt-affected farmland, using survey data from 252 farm households in three agro-ecological zones of Punjab, Pakistan. An accelerated failure time model is used to investigate factors that affect the speed of adoption and the propensity score matching method to evaluate the impact of gypsum adoption on crop yields. About 56% of farm households adopted gypsum, and the average time to adoption was 4.3 years. Key factors reducing the time to gypsum adoption include secure and legal land entitlements, exposure to demonstration trials and field days, access to extension services, and access to credit facilities. In contrast, the distance to soil and water testing laboratories and input markets increases the time to adoption. On average, gypsum adoption increased wheat and rice yields by 17% and 23%, respectively. Our findings suggest that gypsum adoption will increase with the implementation of policies that increase land managers' exposure to the technology and formal information about the technology, reduce barriers to credit access, and provide secure and legal land entitlements.

Introduction

Soil salinization is a major cause of soil degradation in arid and semi-arid regions of the world (Pennock et al., 2015). Soil salinization - in the form of saline (i.e., electrical conductivity (EC ≥ 4 dS m^-1), pH < 8.5, and exchangeable sodium percentage (ESP < 15)), saline-sodic (i.e., EC ≥ 4 dS m^-1, pH ≥ 8.5, and ESP ≥ 15), and sodic soil (i.e., EC < 4 dS m^-1, pH > 8.5, and ESP ≥ 15) - refers to excess of sodium ions (Na⁺) or salts in the soil that restructures the soil’s physical properties, causing slaking, swelling, and hardening of the soil pan (Qadir et al., 2007, Shahid et al., 2018). It can result from climatic variability (i.e., irregular rainfall and evaporation) or a lack of drainage in irrigated lands and can be intensified by using brackish groundwater for irrigation (Ghafoor et al., 2012, Jesus et al., 2015, Kijne, 1996, Qadir and Oster, 2004, Qadir et al., 2014). Soil salinization negatively affects plant growth (Ashraf, 2009, Katerji et al., 2009, Qadir et al., 2000, Semiz et al., 2014) and imposes environmental and economic challenges on farm households.

Globally, irrigated salt-affected land spans nearly 100 countries (Qadir and Oster, 2002), accounting for an annual economic cost of about USD 27.3 billion (Qadir et al., 2014). Of the total salt-affected land, about 8% (84.1 Mha) is in South Asia (Shahid et al., 2018). In Pakistan, about one-fourth of the total irrigated area is salinized (13.94 Mha), at an economic cost of about USD 0.26–0.94 billion per annum¹ (Martin et al., 2006). On average, the yields of wheat and rice grown on saline soils in the Indus basin of Pakistan have declined by 32% and 48% compared to those grown on non-saline soils (Qadir et al., 2014). These low yields, coupled with the burgeoning population, are pressuring the Punjab Government to increase cropping areas to improve food supply. In this context, the rehabilitation of salt-affected lands is of growing importance for food security. Farmers feel pressured to adopt soil amelioration or sustainable land management (SLM) practices to increase cropping area and agricultural productivity.

Worldwide, various SLM practices are prescribed to ameliorate salt-affected lands (Panagea et al., 2016), including adoption of gypsum for saline-sodic soils due to its low cost, availability, and ease of application (Amezketa et al., 2005, Rengasamy, 2010). Gypsum enriches soils with calcium ions (Ca²⁺)² that can replace exchangeable sodium ions (Na⁺)³ (Mahmoodabadi et al., 2013). Moreover, gypsum can improve soil stability and porosity and reduce swelling and crusting of soil to enhance soil hydraulic conductivity (HC) and infiltration rates (IR) (Ghafoor et al., 2008, Murtaza et al., 2009). The amount of gypsum required to restore saline-sodic and sodic soils depends on several factors, including the frequency and amount of rainfall, quality of gypsum, severity of the problem, depth of soil to be treated, gypsum requirement (GR) test method, and quality and quantity of irrigation water (Zaman et al., 2018). Studies have shown that high gypsum application rates can significantly reduce soil electrical conductivity (EC) and ESP (Hamza and Anderson, 2003, Hanay et al., 2004).

From 2006–2012, the Punjab Government invested in a community-driven project named ‘Bio-Saline II’, co-funded by the provincial government and the United Nations Development Program (UNDP), to address soil salinization. The project was implemented in three salt-affected districts of the Punjab province, namely Jhang, Sargodha, and Hafizabad. Among the project-led practices, gypsum was introduced on a cost-sharing basis, with a 50% subsidy on gypsum bags to farmers. During the project, gypsum was popular among farmers due to its positive impact on land productivity (Quiroga et al., 2009, Shah et al., 2011).

Experimental research in Pakistan has shown that gypsum application on salt-affected soils improves rice and wheat yields (Ghafoor et al., 2008, Murtaza et al., 2009, Qadir et al., 2001, Zia et al., 2007), improving the livelihoods and food security of farm households. However, gypsum application involves investment costs that could hinder adoption by resource-poor farmers. Understanding the main drivers of gypsum adoption and its impact on crop yields can help researchers, policymakers, and donors to devise context-specific policies and programs to increase diffusion. Farmers are more likely to adopt SLM practices that provide higher expected benefits (crop yields and income) than existing practices (Pannell et al., 2006, Wollni and Zeller, 2007).

Numerous factors affect farmers’ decisions to adopt SLM⁴ practices, including farmer and farm characteristics, practice attributes, land tenure security, market access, information access, and credit access (Adimassu et al., 2012, Ajayi et al., 2007, Kassie et al., 2015, Sietz and Van Dijk, 2015, Teklewold et al., 2013). Few studies have investigated the factors affecting the time until adoption of new SLM practices, such as natural resource-conserving agricultural technologies in the United States (Fuglie and Kascak, 2001), soil conservation tillage in Australia (D’Emden et al., 2006), and zero-tillage (ZT) in Syria (Yigezu et al., 2018). Studies on the use of gypsum to rehabilitate salt-affected land are limited to experimental studies (Ghafoor et al., 2008, Murtaza et al., 2009, Qadir et al., 2001, Zia et al., 2007). None of these studies has investigated factors that reduce the time to gypsum adoption, which could help policymakers to devise context-specific interventions for salt-affected soils in Punjab and similar agro-ecological regions elsewhere.

The present study investigates the factors affecting the speed of gypsum adoption in three agro-ecological zones (i.e., rice–wheat, maize–wheat–mix, and cotton–mix) of Punjab (Ahmad et al., 2019) and its impact on crop yields, particularly wheat and rice, given their importance of these crops as staple food in the country. This study contributes to the literature on agricultural innovation adoption by (1) investigating the application of gypsum to rehabilitate salt-affected lands, and factors that could influence the time until adoption in a non-experimental data setting, and (2) testing the hypothesis that gypsum adoption improves rice and wheat yields across the three agro-ecological zones. This study also contributes to a broader policy discussion on soil salinization in line with the United Nations Convention to Combat Desertification’s (UNCCD’s) Land Degradation Neutrality (LDN) framework, which is integrated into the Sustainable Development Goals (SDGs) target 15.3 (Orr et al., 2017). The LDN framework aims to achieve a land-degradation-neutral world by 2030 by maintaining and restoring land-based natural capital (Desa, 2016).